The homeless population in New York City has jumped sharply over the last year, causing a record number of people to enter the shelter system. The increase has forced the Bloomberg administration to open nine more shelters in just the last two months — sometimes with only a few weeks’ notice to surrounding neighborhoods.


The administration said the increase stemmed in part from the end of the city’s main rent-subsidy program for homeless families. But the new shelters — five in the Bronx, two in Manhattan and two in Brooklyn — have provoked criticism from local officials who say they were blindsided by the decisions to open them.


The city, for example, relied upon its emergency authority to turn two residential buildings on 95th Street on the Upper West Side of Manhattan into shelters that will eventually house about 200 adult couples, officials said. The buildings had recently been used as illegal hotels before they were shut down, and they still have some long-term tenants.


The city’s Department of Homeless Services told the community board about its plan in mid-July, only two weeks before people began moving in.


The commissioner of homeless services, Seth Diamond, said in an interview that the city had no choice but to open the shelters, given the demand. The city recorded 43,731 homeless people (25,475 adults and 18,256 children) in the shelter system this week, up 18 percent from the 37,143 (21,807 adults and 15,336 children) a year ago, officials said. “We do have to move quickly, and we have to always make sure that we have enough capacity,” Mr. Diamond said. “The one thing we cannot do is have families come in and not have a place for them.”


Mr. Diamond said he did not believe that his department had deceived neighborhoods by opening shelters with little notice, saying the process for picking the sites had been done “always with community communication.”


The administration is not legally obligated to get the approval of community boards before opening shelters, but its policy requires it to tell them of its plans ahead of time.


Of the nine new shelters, the city opened three, including the two in Manhattan, under its emergency authority, giving little notice before proceeding. Several of the other shelters were opened under normal practices but officials had moved quickly. The city told a community board in the Bronx this week that a 50-unit homeless shelter would open within days.


By law, the city is obligated to supply shelter to people who have nowhere else to go, though there are limits to how long they can stay in certain shelters.


The current shelter census is the highest ever, officials said; the number does not represent the total homeless population in the city, because some people avoid the shelter system.


Local officials and neighborhood leaders acknowledged the need for the shelters, but said the Bloomberg administration had moved too abruptly.


Several elected officials sponsored a protest this week in front of the 95th Street buildings, which are side by side between West End Avenue and Riverside Drive. The buildings are privately owned, and the city is paying roughly $3,300 a unit a month, with two or three people living in each unit.


Manhattan’s borough president, Scott M. Stringer, said, “This is no way to meet the needs of vulnerable citizens in this city by simply packing in hundreds and hundreds of people in the dead of night without a long-range plan.”


Asked what the alternative should be, Mr. Stringer, a Democrat who is likely to run for mayor next year, said, “Well, that is the conundrum.” He added: “You still need to come to various constituencies to support a long-term policy to meet a need that is expanding. It’s easy to throw 400 people in a community without doing your homework.”


Other community leaders said they feared that the administration was rushing to find beds for homeless people without first ensuring that there were adequate social services for them. If not properly supervised, they said, the shelters can become rife with drugs and crime.


“It isn’t because we don’t want them in our backyard,” said Mark N. Diller, who is chairman of Community Board 7 on the Upper West Side. “It’s that we don’t want a failure in our backyard.”


A 10-year resident of one of the buildings, Masako Koga, 48, said she noticed new security guards on Monday and was then informed for the first time that homeless people would soon be moving in. “There are so many vacant rooms, though, so I knew it would be coming soon,” Ms. Koga said.